Loud speaker construction



I q Dec. 19, 1933. A, HUNTER I 1,939,898

LOUD SPEAKER CONSTRUCTION Filed Nov. 14, 1930 l N VEN TOR.

MWQJ.#M aww mh ATTORNEYS,

III-Ir 25 mit.

Patented Dec. 19, 1933 I UNITED STATES 1,939,898 I LOUD SPEAKER,CONSTRUCTION Theodore A. Hunter, Cincinnati, Ohio, assignor to TheCro'sley Radio Corporation, Cincinnati,

" Ohio, a corporation of Ohio Application November 14, 1930 Serial No.495,603

3 Claims.

My invention'relates and is applicable to loud speakers in general," andits fundamental object is to secure more power by increasing theeffective magnetization ofthe armature; In addition,

v in constructions embodying my. invention, I gain certain mechanicaland electrical advantages which will be more fully set forthhereinafter,

and which alsoconstitute objects of my invention; These and otherobjects will be entirely epparent to those skilled in the art from the,en-

suing description inconnection with which reference is now made to thedrawing forming part hereof.

g In this drawing:

Figure l-is a sectional view of an exemplary embodiment of my invention;

Figure 2, is. a plan view of an armature employed inthe speaker of.Figure 1.

Fig. 3 is a plan view of a modified armature.

29 In loud speakers it is relatively easy to produce a field of thepower desired, either by means of permanent magnets or by anelectromagnetic field assembly, which for obvious reasons is to bepreferred wherever the circumstances will per- It is not so easy toproduce a powerful excitation of the armature. It is desirable, of

course, to have as close a magnetic coupling as possible between thearmature itself and the voice coil or coils. In endeavoring to secure aspowerful a magnetic excitation of the armature as can be obtained, anobvious expedient is to increase the size of the voice coil. This is notalways possible, due to space requirements in the motor.

Were there no physical limitation on the size of the voice coil,however, its size could not be-made very large Without a certainattendant disadvantage as follows: Since the armature is actuatedprimarily by a fluctuating or alternating currentthe number of turns ina voice coil can- 4 not in many instances be made very large withoutgiving the coil an impedance which materially reduces the value of theactuating current. The effect is heightened the closer the couplingbetween the coil and the armature.

The problem, then, is to secure .the largest effective number of ampereturns in an armature voice coil assembly before the limiting value ofimpedance is reached. I have discovered that this problem may be met,and the object attained through employing a plurality of voice coilslocated essentially upon different magnetic .portions of the armature,and distributing through these coils a relatively large number of ampereturns. The useful magnetic effect of the several coils may be madeadditive, while the combined impedance is markedly less than would bethe case if the same number of ampere turns were placed in a less numberof coils or a single coil.

The employment of a number of voice coils as set-forth requires andfacilitatesa different conn. struction of. armature' from those hithertoemployed. In a preferred embodiment of, my invention, I provide anarmature having a series of arms upon'a plurality of which I mount voiceI coils in such a way as. to produce an additive as magnetic effect inthe armature-while having a total impedance much less than if the samenum- .ber of ampere turns were employed. In some instances this type ofarmature permits me, as hereinafter to be explained, to provide a returnpath for the alternating flux of the armature, whichpath doesnotcoincide with the, fieldflux in the field structure. I. r

In the exemplary embodiment of my invention shown in the drawing, I haveindicated a field structure comprising a pair of cup-shaped members land 2 having central posts 3 and 4 forming pole pieces. The cup-shapedmembers have flanges 5 and 6 out-turned upon their edges. The flangesare perforated for the reception of bolts 7 30 at intervals, and thesebolts are used to fasten the cup-shaped members together in opposedrelationship. An armature 8 is mounted in this assemblyby being clampedbetween the flanges, so that its central portion lies between the poleends 5 of the posts 3 and4. The ends of these posts are interspacedsufficiently to permit the central portion of the armature to vibrate.Within each cupshaped member I have shown circular field coils 9 and 10surrounding the posts 3 and4. These 99 will be so connected to a sourceof direct current I as to magnetize the pole pieces 3 and 4 strongly,and to give them an opposite magnetic polarity. Voice or armature coils11 are mounted upon the armature, as will be more fully explained. Theyare so connected that they have a combined effect in magnetizing thearmature with a magnetic pole at the center thereof. Thus the centralportion of the armature will be attracted toward the field pole piece 3or 4, whichever is of the opposite 1 00 polarity, and will be repelledfrom the outer pole piece. The strength of the attraction and repulsion,for a given strength of field, will be proportionate to the magneticforce produced in the armature by the voice or armature coils; and ifthe 195 current in these coils is fluctuating or alternating incharacter, the armature will vibrate inaccordance therewith. Thepost 4is provided with a perforation 12, through which passes a drive rod 13..At one end this rod is connected to the armature 8, and at the otheritmay be connected to a cone 14 or other vibratile device, eitherdirectly, or

' through some suitable motion transmitting device.

My armature may center itself through itsown resilience, or separatecentering means may be employed. It will be noticed that the particulartype of construction shown enablesme to produce a motor which iscompletely self-contained andis dust-proof. It will be understood that Ihave omitted to show mounting means for my motor body and such otherconstructional details as are not necessary to a complete'understandingof my invention.

My armature, in its preferred form comprises a central portion 8a and aplurality of arms 81) radially disposed with reference to the centralportion. The voice coils 11 are mounted upon these I were the samenumber of ampere turns placed in one or two coils, as has been thepractice hitherto. It is also less than'would bethe case were the coilsall located together upon the same magnetic portion ofthearmature. Bythis means Iiam able to employ more ampere turnsand' secure a strongermagnetization'of my armature for any given excitation current before theimpedance in thearmature cuts down the useful value of the im-' pressedcurrent. v V

In another construction shown in Fig. 3, partie ularly a construction inwhich the number of the" radial arms 8b is even, I may mount coils 15upon alternate arms 16, the intervening arms 17, which in this instanceare not provided with voice coils,

serving as return means for the alternating ory fluctuating flux in thearmature, the" path being completed between arms by the clampingportions or flanges of my field assembly.- Thus a path is provided forthe armature flux" which does not.

coincide with the path of the field flux. I

Modifications may be made in my invention" 'without departing.fromthe-spirit thereof; and

my-invention maybe adapted to motors of different types than that shownin the exemplary embodiment described. I

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent, is:+-

1. Ina loud speaker, a vibrating armature having'a plurality of magneticvibrating portions, and

voice'coils mounted upon'more than two of said portions.

2. In a loud speaker, a vibrating armature havj inga centralportion,-and radial arms forming part of the vibratile system,and voicecoils mounted cnm'ore than two ofsaid arms, said voice coils beingconnected soas to produce a cumulative magneti'ceffect upon one portionof said arma- V ture.f

' 3. The. loud speaker, an' armature having a central portion, and aplurality of radially disposed arms, voice coils mounted on some ofsaidarms,

other of said arms adapted to form a return path for the magnetic fluxin said armature, and mounting means connecting the outer ends of saidarms to complete the magnetic circuit.

THEODORE A. HUNTER.

